The present invention is directed to a capacitor discharge ignition system and more specifically to a capacitor discharge ignition system having automatic spark advance with engine speed, force commutation of the electronic switch in the ignition circuit, automatic speed compensation for variations in temperature and lamination gap, prohibition of engine reversal and an extremely low impedance manual shutoff.
Capacitor discharge ignition systems are well known in which a flywheel magnet is rotated into and out of flux cutting proximity to one coil for effecting the charge of an ignition capacitor and to another coil for effecting the triggering of an electronic switch discharging the ignition capacitor through a high voltage transformer to a gap ignition device of the engine. Such systems generally require the physical displacement of the charging and trigger coils to thereby provide the necessary timing between the charging and discharging of the capacitor responsively to engine rotation.
Attempts to place both the charging and trigger coils on the same core lamination have generally required that the waveforms be 180 degrees out-of-phase to achieve the necessary temporal displacement of the positive components of the current waveforms induced in the two coils. Out-of-phase waveforms, however, are a disadvantage in that the second wave component of the four major wave components of an induced waveform is the component with the greater energy. The second component is thus far more desirable for both charging and triggering purposes. Inversion of one of the waveforms requires the utilization of the third wave component for either the charging or triggering function.
Attempts to utilize in-phase charging and trigger waveforms on the same core lamination generally results in switch conduction as a result of the trigger coil waveform during the time interval during which energy is available from the charging coil to charge the ignition capacitor. Unless, however, the energy in the charging current waveform can be accumulated and suddenly released through the high voltage transformer, the potential applied to the ignition device will not be sufficient for gap ionization and the engine cannot run.
It is accordingly an object of the present invention to provide a novel method and capacitor discharge ignition system utilizing in-phase charging and trigger coil waveforms so that the high energy content of the second wave component may be utilized for both charging of the ignition capacitor and for triggering the electronic switch effecting the discharge thereof.
The utilization of in-phase charging and trigger waveforms may be made possible in the present invention by the back biasing of the electronic switch immediately after the discharge of the ignition capacitor so that the ignition capacitor may be again charged by the same wave component that effected triggering of the electronic switch. It is accordingly a further object of the present invention to provide a novel method and capacitor discharge ignition circuit which automatically effects the back biasing of an electronic switch in the ignition circuit immediately after the firing thereof.
Another problem in the utilization of SCRs in capacitor discharge ignition systems has been the difficulty in insuring that the SCR immediately turns off after discharge of the ignition capacitor. Failure of the SCR to turn off prevents charging of the capacitor to a potential sufficient for gap ionization of the ignition device. It is accordingly another object of the present invention to provide a novel method and apparatus for force commutation of the SCR to insure the nonconduction thereof immediately after discharge of the ignition capacitor.
It is also a desiratum that the time of occurrence of the spark of an internal combustion engine be advanced with an increase in engine speed, i.e., that the spark occurs earlier in the engine cycle as the speed of the engine increases. It is yet another object of the present invention to provide a novel method and circuit for automatically advancing the spark current of a capacitor discharge ignition system as a function of engine speed.
Capacitor discharge ignition systems are frequently utilized on machinery such as chain saws and the like in which operation of the engine at an excessive speed is detrimental to engine longevity. It is thus desirous that engine speed be limited for design considerations to a predetermined maximum. It is yet a further object of the present invention to provide a novel method and capacitor discharge ignition circuit in which the frequency of spark occurrence is automatically limited as a function of engine speed to thereby limit the speed of the engine.
Variations in ambient temperature and in the spacing of the legs of the laminated core on which the charging and trigger coils are mounted near the flywheel magnet vary the timing of the ignition circuit and thus produce variations in engine speed which are undesirable. It is still a further object of the present invention to provide a novel method and capacitor discharge ignition circuit for automatically compensating a capacitor discharge ignition system for variations in temperature and in lamination gap. It is yet still a further object of the present invention to effect the automatic compensation for variations in lamination gap despite even the intentional twisting of the core by an operator for the purpose of varying engine speed.
As described and claimed in the copending application Ser. No. 514,603 filed Oct. 15, 1974, by the assignee of the present invention, a coil may be provided to generate a waveform in-phase with the charging coil waveform for the purpose of insuring electronic switch conduction during the time interval when the capacitor is normally charged. Shut-off of the engine is thus achieved. However, a problem may arise in that the manual switch contacts utilized to selectively couple the shutoff coil into the circuit are often subject to an accumulation of moisture laden debris such as sawdust. It is yet still another object of the present invention to provide a novel method and capacitor discharge ignition system shutoff apparatus which requires an extremely low impedance manually operable switch. The likelihood of the inadvertent effecting of engine shutoff by such debris is thus significantly reduced.
Still yet another object of the present invention is to provide a novel method and capacitor discharge ignition circuit in which shutoff of the engine may be achieved without the utilization of a shutoff coil and without the interruption of the circuit between the charging coil and the ignition capacitor.
It is generally undesirable for an internal combustion engine to operate in alternative directions and it is yet still another object of the present invention to provide a novel method and capacitor discharge ignition system in which engine reversal is automatically prohibited.
These and many other objects of the present invention will become apparent to one skilled in the art to which the invention pertains from a perusal of the following detailed description when read in conjunction with the appended drawings.